[urq] Help Needed -- 1988 5000KSQ

[Ben Swann]

Steve,

AFAIK there is no real way pulling the codes will indicate a marginal or failing O2
sensor - only if the signaling is out of range or bad wiring/short/sensor voltage way
out of tolerance.   If however the O2 sensor is failing in such a way that it is giving
a "false" signal voltage, the ECU only knows to compensate by enriching or enleaning to
compensate which may be the opposite of what it should be doing.    I've seen this
happen and sometimes a Q&D way of telling is if pulling the wire has the car back to
good running when in closed loop (engine warm).

If anyone knows differently then please advise.  I know many newer vehicles have some
self-diagnostics availble for certain sensors, but I don't thing this is applicable to
the older single and 3 wire O2 sensors.

I do concur that O2 sensor is suspect and the irony is that a failing one won't
necessarily gen a code which may lead one to believe that is it OK.

Ben

[Date: Mon, 28 Jul 2008 07:15:37 -0700
From: "urq" <urq at pacbell.net>
Subject: RE: Help Needed -- 1988 5000KSQ
To: <quattro at audifans.com>
Message-ID: <023601c8f0bc$9cc31e50$d6495af0$@net>
Content-Type: text/plain;	charset="iso-8859-1"

IMO the symptom that the engine runs well until it warms up has me siding
with those saying OXS ... but the first thing to do is to read the codes
from the ECU ... there should be OXS codes if this is the culprit ... 

That said, going forward with the intake tract leak ... my first suspect
would be the crankcase vent hose that runs down from the valve cover on the
spark plug side of the engine.  The original post indicated that there was
some work at the back of the engine compartment done recently, and the cast
rubber piece that attaches to the crankcase vent can deteriorate to the
point where it is easily damaged.  IME, when this hose goes you can get
enough of an intake leak to cause the engine to stall under power.  

Steve B
San Jos?, CA (USA)]